Time-sharing or dividing attention among multiple tasks is an important component of many activities such as piloting. But time-sharing is a complex skill that may be particularly prone to the adverse effects of aging and attentional limits. The proposed research focuses on the effects of aging on pilot time- sharing performance. Pilots are considered to have a level of expertise in time-sharing that would not have developed over the course of a typical laboratory study. Pilot performance therefore provides an opportunity to examine the potential of expertise to compensate for the age effects. A four-factor theoretical framework has been proposed to account for time- sharing performance. In addition to age and expertise in time- sharing, the composition of the time-shared tasks and attentional resources are hypothesized to influence time-sharing interactively. Two aspects of time-sharing performance are studied: (a) time-sharing efficiency or the level of dual task performance attained and (b) resource allocation or the degree to which subjects can flexibly deploy limited attentional resources as task priority or urgency dictates. Earlier research has demonstrated age-related time- sharing decrements for attention- demanding tasks and partial expertise compensation for age effects. The proposed research examines the extent to which age effects are modifiable by experience in a more flight domain- specific time-sharing condition. Further, mechanisms of the age- related declines and expertise compensation are explored. The research has important theoretical and practical implications. A validated theoretical framework can help elucidate the properties of attentional resources and to help predict time-sharing performance. The proposed research also contributes to a scientifically derived database of pilot performance that should have important implications pertinent to the Age 60 rule that prohibits commercial airline pilots age 60 or above to be the pilot-in-command. Other practical implications include the design of age-independent diagnostic tests for time-sharing decrements, and the specification of training or skill maintenance requirements.